Ask them if they believe God is omniscient. The typical answer will be that they do; it can then be argued that he knows the future, he is not planning the future. This can also be worked into Waldheri's argument that since he knows the future he knew you were going to be an atheist, so nothing they can say will change that.

Also once omniscient is on the table you can have some fun with the other omni's; and even try using the Epicurus quote.

Let's throw in suicide. The ultimate sin. Suicides got straight to hell, correct? Was this God's plan? Does it "change" God's plan for everyone effected by said suicide? There can't be a "plan" if we can just fuck up God's all mighty plan. Or maybe God planned the suicide & sent some poor bastard to hell for the common good of everyone else... Fuck that.